Work tables having adjustable surfaces are well-known. Typically, such tables comprise a stand which has a work surface which can be vertically and angularly adjusted to align with an operator's line of vision. There is disclosed in U.S. Pat. No. 3,690,608 an adjustable stand comprising a telescopic vertical upright having a tilting mechanism at the top for supporting a table assembly in pedestal fashion. The tilting mechanism includes a worm gear which meshes with a gear wheel connected to the table assembly.
Several problems attend the operation of this type of stand. Because the worm gear supports the work table assembly and acts directly against the gear wheel carried thereby, the mechanical advantage gained from the mechanism is fixed at a one to one ratio. Further, the mechanism does not operate easily over the complete range of adjustment, varying in ease of operation with load distribution and the angular position of the table. Resultingly, the worm gear may prove difficult to turn at times.
Other shortcomings are inherent in this and other known work stands. The mechanical advantage attained by the tilt mechanism cannot be varied or tailored over the operating range of the mechanism. Further, the table axis of rotation and the rotary actuator crank axis are not coincident, making adjustment inconvenient. Finally, pedestal support of the table assembly does not provide a high level of torque restraint, resulting in a table assembly which is susceptible to undesirable movement from vibrations.
Surfaces are also known to be made vertically adjustable through operation of a scissor-type linkage. U.S. Pat. No. 3,611,453 discloses an adjustable bed having side mounted scissor-arms for elevating and tilting a bed surface forward and backward. Such known adjustment mechanisms, however, are cumbersome to operate and are ill-suited for work stands requiring leg room beneath the table surface. Moreover, such table assemblies do not provide for economic sharing of components between angular and vertical adjustment mechanisms, without sacrificing the operating independence of each mechanism.